Process for copolymerizing conjugated dienes

ABSTRACT

A DIENE OF 4 TO 6 CARBON ATOMS AND STYRENE OR OTHER VINYL AROMATIC MONOMER, INCLUDING ALKYLATED VINYL AROMATIC MONOMERS, ARE COPOLYMERIZED IN A HYDROCARBON SOLVENT USING A SUBSTANTIAL AMOUNT OF EACH MONOMER AND UTILIZING AS THE CATALYST, ALKYLLITHIUM AND POTASSIUM HYDROXIDE. THEY MAY BE ADDED SEPARATELY OR MAY BE COMPLEXED BEFORE BEING ADDED TO THE REACTION MIXTURE. THE RESULTING COPOLYMER IS A COPOLYMER OF SUBSTANTIALLY CONSTANT COMPOSITION (I.E. A COPOLYMER CONTAINING NO SUBSTANTIAL BLOCK OF VINYL MONOMER); AND IT HAS SUBSTANTIALLY THE MICROSTRUCTURE OF A NORMAL POLYMER INITIATED BY AN ORGANOLITHIUM CATALYST. THE DIENE MAY BE BUTADIENE, ISOPRENE, PIPERYLENE OR 2,3-DIMETHYLBUTADIENE OR A MIXTURE THEREOF. THE VINYL AROMATIC MONOMER MAY BE STYRENE OR AN ALKYLATED STRYRENE OR VINYL NAPHTHYLENE OR ALKYLATED VINYL NAPHTHYLENE OR A MIXTURE THEREOF.

United States Patent 3,767,632 PROCESS FOR COPOLYMERIZING CONJUGATED DIENES Adel F. Halasa, Bath, Ohio, assignor to The Firestone Tire & Rubber Company, Akron, Ohio Continuation-impart of abandoned application Ser. No. 761,831, Sept. 23, 1968. This application May 3, 1971, Ser. No. 139,804

Int. Cl. C0815 19/06, 19/08 US. Cl. 260-83.7 3 Claims ABSTRACT OF THE DISCLOSURE A diene of 4 to 6 carbon atoms and styrene or other vinyl aromatic monomer, including alkylated vinyl aromatic monomers, are copolymerized in a hydrocarbon solvent using a substantial amount of each monomer and utilizing as the catalyst, alkyllithium and potassium hydroxide. They may be added separately or may be complexed before being added to the reaction mixture.

The resulting copolymer is a copolymer of substantially constant composition (Le. a copolymer containing no substantial block of vinyl monomer); and it has substantially the microstructure of a normal polymer initiated by an organolithium catalyst. The diene may be butadiene, isoprene, piperylene or 2,3-dimethylbutadiene or a mixture thereof. The vinyl aromatic monomer may be styrene or an alkylated styrene or vinyl naphthylene or alkylated vinyl naphthylene or a mixture thereof.

This application is a continuation-in-part of my application Ser. No. 761,831 filed Sept. 23, 1968, now abandoned.

This invention relates to an improvement in the copolymerization of a conjugated diene containing 4 to 6 carbon atoms with styrene or other hydrocarbon monoxinyl aromatic monomer. The catalyst used is an alkyllithium with potassium hydroxide, often as a complex.

The use of potassium hydroxide with an alkyllithium as a catalyst for the preparation of butadiene-styrene, etc. copolymer increases the rate of polymerization of the styrene with the butadiene so that a copolymer of constant composition is formed. The microstructure of the diene portion of the copolymer remains substantially constant. No gel is formed. When the content of styrene in the polymerization reaction mixture is greater than 18 percent and the ratio of the moles of potassium in the catalyst to the moles of lithium is at least 1.00, no block styrene is formed. When the styrene content is below 18 percent, no block styrene is formed regardless of the Li/K ratio. The copolymer contains substantially the same amount of styrene as added to the reaction mixture. In this respect the use of KOH is different from the use of alkali metal alkoxides with an alkyllithium (as disclosed in Wofiord US. 3,294,768) because in such prior art the vinyl-content of the polymer produced varies with the Li/ K ratio. The fact that the vinyl-content is substantially constant in the process of this invention simplifies the control of the process. Thus, the polymer produced by this process has several advantages. It is useful as a replacement for butadienestyrene, etc. copolymers prepared by other methods.

A complex is usually formed by heating a substantial amount of the complexing potassium hydroxide with the akyllithium initiator in the absence of air, and preferably 3,767,632 Patented Oct. 23, 1973 in an inert solvent, such as an aliphatic hydrocarbon solvent or benzene or toluene. A mixture of alkyllithium initiators may be used. The complex can be recovered and stored or shipped if kept out of contact with air.

The conjugated diene may be butadiene-1,3, isoprene, piperylene or 2,3-dimethylbutadiene-1,3 or a mixture thereof.

The vinyl aromatic monomers which may be used include, for example, styrene, alpha-methyl styrene, vinyl toluene, vinyl naphthalene, 3,5-diethylstyrene, 2,4,6-trimethylstyrene, 2-ethyl-4-benzylstyrene, 4-p-tolylstyrene, 4 (4 phenyl n butyl)styrene, 4-methoxystyrene, 3,5- diphenoxystyrene, 3 decoxystyrene, 4 dimethylaminostyrene, 4,5-dimethyl-l-vinylnaphthalene, 3-ethyl-1-vinylnaphthalene, 2,4 diisopropyl 1 vinylnaphthalene, 3,6- di p tolyl 1 vinylnaphthalene, 6-cyclohexyl-1-vinylnaphthalene, 8 phenyl l vinylnaphthalene, 6-benzyl- 2-vinylnaphthalene.

The alkyllithium initiators that may be used are Well known and include those mentioned in US. Pat. 3,317,- 918 which is included herein by reference as disclosing alkyllithiums useful as initiators as well as known methods of producing copolymers of butadiene or isoprene with styrene, etc., including known temperature ranges and amounts of hydrocarbon-lithium initiator. From 0.1 or 0.5 or preferably 1.0 to 10 or even 15 or 20 mols or greater amounts of potassium hydroxide may be used per mol of the alkyllithium initiator. Any usual initiator amount of alkyllithium will be used, such as from 0.001 to 0.5 part of lithium per parts of monomer.

The polymerization may be carried out at any temperature customarily used for such polymerizations, usually just below the boiling point of the solvent, but other temperatures may be employed usually between about 50 F. and 266 F. Atmospheric pressure will generally be employed, but pressures above or below atmospheric may be used.

The invention is illustrated by the following examples.

The drawing illustrates results obtained in carrying out Example 6.

EXAMPLE 1 The initiator complex is advantageously prepared by heating 1 molar equivalent of the complexing potassium hydroxide with 5 to 10 molar equivalents of the alkyllithium. It should be understood that the amount of the complexing compound is used in excess of that which enters into the reaction. The complexing is advantageously done in an inert solvent. The following is illustrative:

To a 400-ml. solution of n-butyllithium (0.30 mmole per ml.) containing mmole of n-butyllithium there was added 100 mmoles of potassium hydroxide. The flask was then shaken vigorously for several hours. The potassium complexed with the lithium in the n-butyllithium. The solution turned deep wine red. This contained substantially equimolar parts of lithium and potassium. There was undissolved and unreacted potassium hydroxide in the bottom of the solution. It is not necessary to separate this, but usually the solution of the complexed initiator will be decanted from such a residue. The complexed initiator may be separated from the solvent if it is to be stored or shipped. Such recovery will be attended with precaution.

EXAMPLE 2 A solution was prepared of 400 milliliters of 25-percent isoprene in heptane. This was divided equally in eight 3 bottles. Then 17.5 ml. of distilled styrene was added to each bottle. The bottles were catalyzed with 1.0 ml. l.50 mmole) of n-butyllithium (BuLi) and the amounts of potassium hydroxide listed in the following table:

TABLE I Randomizing agent BuLi, BuLi KO H, K011, ml. rnrnolo ml. mmole 1.0 1. 5O 0. 30 0. B1 1. 1. 50 0.50 1. 35 1. 0 l. 50 0. T 2. l6 1. 0 1. 50 1.0 2. T0 1. 0 1. 50 2. 0 5. l. 0 1. 50 3. 0 8. 00 1.0 1.50 4.0 10.80 1. 0 1.50 5. 0 13. 50

block copolymer was found.

TABLE II (Dis-1,4, Trans-1,4, Trans-3,4, Styrene,

Bun percent percent percent percenfi D.S.V.

71. 6 16. 3 12. CI 30. 2 O 50 71. 7 16. 0 12. 3 30.1 0 51 72. 9 14. 9 l2. 2 27. 7 0. 51 71. 5 16. l 12. 2 29. 7 0. 52 71. 5 15. 5 13. l 30. 8 O. 54 71. 7 15. 1 13. O 29. O 0. 54 71. 7 15.1 13.0 28. 8 0. 60 71.. 0 15. 5 13. 4 32. 5 0. 67

By infra-red analysis.

EXAMPLE 3 Four bottles were charged with 400 m1. of 30-percent butadiene-1,3 in hexane and ml. styrene. The reaction was catalyzed with 1.0 mmole of n-butyllithium (BuLi) with varying amounts of potassium hdyroxide as given below.

KOH BuLi, Run mmole M1. Mmole A 1. (l 0. 20 0. 54 B 1. 0 0. 4O 1. 08 C 1. O 0. 60 1. 12 D l. 0 1. 0 2. 7

The bottles were placed in a 50 C. bath for 12 to 16 hours. The reactions were terminated and the products analyzed, with the results recorded in the following table:

TABLE 111 Block Trans=1,2 styrene, Styrene, Run percent percent D.S.V. Gel percent 9. 6 14. 07 1.27 None 28. 4 10.7 7.27 1 05 d0 30.6 12.2 None 1.33 clo. 28.0 12.0 None 1.84 do 28.5

Polymerization with butyllithium in the absence of KOH produces a higher percentage of block copolymer than recorded in the above table. The table shows that by using sufiicient KOH, substantially no block copolymer was produced when the ratio of Li/K was over 1.00. The

percent of 1,2-unsaturation remained substantially constant when no block copolymer was formed.

EXAMPLE 4 Fifteen hundred grams of butadiene (25%) in hexane was charged into a one-gallon reactor. n-Butyllithium (5.0 mmole) and KOH in mineral oil (10.0 mmole) were added initially. Styrene grams) was also added.

The batch was heated to 200 F. for polymerization. Samples A and B were taken after 10 minutes and after 30 minutes. They were cooled to room temperature. Both samples were dried and analyzed for the content of the different stereo polymers and for styrene. The results are recorded below.

TABLE IV Percent Sample (Sis-1,4 Trans-1,4 Tra ns-1,2 styren No block styrene was formed. No gel Was formed. There was no substantial change in the stereo structure of the copolymers.

EXAMPLE 5 A one-gallon reactor equipped with mechanical stirrer driven by an electric motor was charged With 1500 g. of 25% 1,3-butadiene in heptane solution. To this was added 100 g. of styrene. This was catalyzed with 6.0 mmole nbutyllithium and 15 mmoles of KOH in mineral oil emulsifier. The temperature of the polymerization was adjusted to 200 F. and allowed to polymerize till 100 percent conversion was obtained in 3 hours. The polymer was removed from the reactor and stabilized and dried on the drum drier. The polymer was then analyzed by nuclear magnetic resonance, infra-red spectroscopy and refractive index and was found to be of constant composition, i.e. without any blocks. The product contained no free styrene or gel. The copolymer had the following content of stereopolymers and styrene:

TABLE V Percent (Dis-1,4 Trans-1,4 Trans-1,2 Styrene EXAMPLE 6 Polymerizations were run using a constant ratio of butyllithium to potassium hydroxide at 90 F., F. and P. All were run with a monomer content of 65 percent butadiene and 35 percent styrene, in hexane, at the same level of potassium hydroxide. At the lowest polymerization temperature, there was a very rapid up take of styrene and many points on the curve show a styrene content exceeding the initial 35 percent. By increasing the temperature to 150 F., the addition rate of the styrene decreased, and at 180 F., the KOH has substantially no effect on the rate of styrene addition.

Thus, the beneficial effect of the potassium hydroxide on the polymerization is evident more particularly within the temperature range of 50 to 266 F.

1 claim:

1. The process of copolymerizing a conjugated diene containing 4 to 6 carbon atoms and a hdyrocarbon monovinyl aromatic monomer and producing a copolyrner, the diene portion of which is of substantially constant 1,2- content, which process comprises polymerizing said monomers in an inert solvent at 50 to 266 F. in the presence of a catalyst which consists of alkyllithium and potassium hydroxide and producing a copolymer which is substantially free of block vinyl aromatic monomer by using monomers with a vinyl aromatic content of at least 18 percent in the polymerization reaction mixture with the molar ratio of lithium to potassium in the catalyst being 1:x, x being a number not substantially more than 1 and not over 20, or using any molar ratio when said vinyl aromatic monomer content is less than 18 percent.

2. The process of claim 1 in which the monomers are butadiene and styrene.

3. The process of claim 1 in which the alkyllithium is n-butyllithium.

JAMES A. SEIDLECK, Primary Examiner US. Cl. X.R.

New PUNLTED STA'LES PATENT omen: v

CERTIFICATE OF CORRECTI-QNI Pacem: No 5,7 '73 5 Dated Octobef-Qi 975 Inventor-(s) I Ade'l. Farhan Hnlasa It. is certified that: error appears in theabove-identified patent and that said Letters Patent are hereby corrected as shown below '1 Column '1 Line 37, 'finonoxinyl" should read --monoviny1--, Column 5, Line 2e, in Table II, the heading; crane 4th column which reads "Trans-5,4, percent" should read 5,4, percent--.. Column 4, Line '17, in Table IV, the heading of the #th column which reads "Tra ns-rl ,2" should read -1 ,2-'--.

Column Line 4 in Table v, the heading oi "the 4th column which reads "Trans-'1 ,2" should read -1 ,2'--.

Column 4, Line 68, "hdyrocarbon" should read hydrocarbon.-

Signed and sealed this 12th day 'ofMa rch 1 974 I (SEAL) Attest:

EDWARD M.FLETCHER,JR. e- 1 e CJMAR SHALL DANN- Attesting Officer Commissioner of Patents 

